Table of Contents
Advertisement
Description and Principle of Operation
Universal Analyzers 600 Series Mini Thermoelectric Gas Cooler is the least expensive, compact Thermoelectric Cooler.
The 600 Series Mini Cooler is available as either a Single or Double Sample Stream providing a self-regulated 4.0°C
Dewpoint Sample Gas ready for Analysis. The 600 Series Cooler provides a Signal output 0-1VDC representing 0-50°C.
An externally mounted 12, or 24VDC Power Supply is required and is offered as an Accessory.
In order to analyze combustion products or incinerator effluents utilizing a direct extractive sampling technique, it is
important to remove the water vapor without removing the water soluble fraction(s) from the gas sample. The heat
exchangers (impingers) used in the Universal Analyzers gas sample coolers are designed to minimize the gas/condensate
area and time of contact to reduce to a minimum, the amount of mass transfer of those water soluble components from
the gas phase into the liquid phase. The result is a dry gas sample which has the same composition on a dry basis before
and after passing through the chiller.
A gas sample is usually taken from a stack with a probe extending into the center of the stack mounted onto or adjacent
to a heated filter. The heated filter is maintained at a temperature above the dew point of the stack gas, usually 300°
to 400°F. in order to avoid cementing the filtered particulates to the filter medium with condensate. A means is usually
provided to automatically blow the particulates trapped by the filter, back into the stack on a periodic basis.
The stack gas sample is clean but "wet" after passing through the filter assembly. The moisture in the gas sample comes
from the fuel as a product of combustion, from the humidity in the air which supports the combustion and from the water
content which was trapped in the fuel. This latter source of water in the sample can be from burning moist coal, wet
garbage, or from water injected into the fire box. Water from all of these sources will remove the water soluble gasses
from the sample stream if allowed to condense in the sample line prior to the controlled separation within the Universal
Analyzers' heat exchangers in the sample cooler.
In order to maintain the temperature of the gas sample above the dew point as it is transported to the gas sample cooler,
a heat traced sample line is usually employed. The heat traced sample line can be very short if the gas sample cooler is
located close to the heated stack filter or it could be several hundred feet long if the gas sample cooler is located in the
analyzer shack some distance from the stack.
The Universal Analyzers gas sample cooler contains the special impinger type heat exchanger(s). These are mounted
within heat transfer blocks which are either passively cooled by ambient air or thermoelectrically cooled using Peltier
elements. Where high water contents are encountered, it is efficient to remove the condensate in two stages, one at
the temperature using a passive heat exchanger and then by pushing the sample into a thermoelectrically cooled heat
exchanger. The passive heat exchanger can remove water which will condense at the temperature of the environment. In
high water content samples, this could be as much as 80% of the water in the sample. The thermoelectrically cooled stage
is temperature controlled at a factory setting of 5°C. This temperature can be adjusted with a set point potentiometer.
The gas sample conditioning system should contain additional components to insure that a clean, dry sample is presented
to the analyzer panel for minimum analyzer maintenance. A sensor should be provided to sense the presence of
condensate, should any exist in the tubing following the chiller. This is the optional WCO (Water Carry-Over) sensor which
can be provided with a Universal Analyzers chiller. A visible coalescing filter which collects particulates on the outside of
the cylindrical filter, surrounded by a transparent bowl will allow the operator to inspect the condition of the heated stack
filter. The WCO sensor can be provided with the sensing elements in the bottom of the filter bowl to provide an early
warning if the coalescing filter removes liquid from the sample stream. This combination filter/moisture sensor is
called the "WCOF".
The location of the sample pump (usually an oil-less diaphragm pump) within the sampling system is the subject of much
debate. If the pump is located upstream from the chiller, it should have a heated head to avoid the presence of a two
phase mixture which shortens the life of a diaphragm and causes maintenance problems. It can be shown that passing
the gas sample through the chiller under a slight positive pressure will result in a lower gas dew point than if the gas were
at a slight vacuum. A common location for the sample pump is in the sample line after the chiller. This allows the sample
pump to handle a cool, dry sample with much reduce maintenance problems. Some design engineers have taken the
approach to use a sample cooler having two chilled heat exchangers. The pump is placed in the sample line between
Page 7 of 25
MAN.600.REVE.06302015
Advertisement
Table of Contents
